Hi,
if someone help me to find out what these two plans should contain specifically.
1. Capacity Plan - where we ensure all the resources are at the capacity to provide services
2. Availibility Plan - as far as I understand this plan contains the availibility of resources to provide services.

please help me understand what is the basic difference between these two.

The Capacity Plan shows how the capacity requirements will be met over the coming period (1-2 years). This takes account of ex[ansion/contraction plans of the business, as well as the technical capacity constraints of indiviual CIs. It shows when additional capacity should be bought (thus allowing it to be budgetted for).
The Availability Plan shows how the Availability commitments in the SLAs will be met. This takes account of eliminating single points of failure, building in resilience, ensuring that the equipment bought is reliable, easily maintained etc. It shows how the balance between MTBF and MTTR is made. (It is perhaps better to have a shorter Mean Time Between Failure, if the device has a short Mean Time to Repair, than a more reliable item which takes days to recover.) The Plan shows the risks to Availability, and the counter-measures required, such as buying UPS/generators in case of power cuts. Availability would work with capacity (unless both roles are combined) to ensure that insufficient Capacity is not a risk to Availablit.
Hope this helps!_________________Liz Gallacher,
ITIL EXPERT
Accredited ITIL and ISO/IEC20000 Trainer and Consultant - Freelance